Flyback output voltage vs. frequency
Dr. Dark Current, Sun Mar 18 2007, 02:09PMI have been experimenting with single MOSFET flyback driver (tl494+mosfet). I could get about 30kv from a small flyback with frequency below 15khz. That was nice, but my ears did really hurt from the horrible whistling sound. When I upped the frequency above audible range, the output voltage decreased (logically). I wanted it to be the same as previously, so I removed some turns from the primary in hope to increase the output voltage. However, whatever I did (vary duty cycle, change primary turns), I did not bring the output voltage even close to as with lower frequency. So the question is, WHY I cannot get so high voltage with higher frequency? Is there something I can do to increase the voltage (change core airgap maybe?)
thanks, J.M.
Re: Flyback output voltage vs. frequency
Myke, Sun Mar 18 2007, 03:04PM
Probibly the flyback's resonant freq was near 15KHz so when you increased the freq then it went out of resononce. Yeah making the airgap larger in the flyback core will decrease the inductance thus raising the resonant freq.
Myke, Sun Mar 18 2007, 03:04PM
Probibly the flyback's resonant freq was near 15KHz so when you increased the freq then it went out of resononce. Yeah making the airgap larger in the flyback core will decrease the inductance thus raising the resonant freq.
Re: Flyback output voltage vs. frequency
Dr. Dark Current, Sun Mar 18 2007, 06:28PM
Wow, I'm now getting maybe 50kv from a small poor ac flyback!
What I did was to increase the airgap maybe 3 times and I also put a resonant capacitor on the primary, it's resonating above audible range, but the problem is now that whenewer I connect anything to the output, it drifts out of resonance and the voltage drops.
Has anyone have an idea how to make this circuit self-resonant? Feedback winding? Secondary return feedback? Antenna? I seem now to have a Tesla coil-like problems
Dr. Dark Current, Sun Mar 18 2007, 06:28PM
Wow, I'm now getting maybe 50kv from a small poor ac flyback!
What I did was to increase the airgap maybe 3 times and I also put a resonant capacitor on the primary, it's resonating above audible range, but the problem is now that whenewer I connect anything to the output, it drifts out of resonance and the voltage drops.Has anyone have an idea how to make this circuit self-resonant? Feedback winding? Secondary return feedback? Antenna? I seem now to have a Tesla coil-like problems
Re: Flyback output voltage vs. frequency
uzzors2k, Sun Mar 18 2007, 08:22PM
Nice, I didn't know that about the air gap, I'll have to try it sometime.
Concerning making the circuit self-resonant, I made this on Friday. Its not done yet, as there is still an issue with the high side mosfet floating, but the concept should work. It is supposed to act like a SGTC, except solid state. When circuit starts the top mosfet will conduct until capacitor C is full, at which point it will close and the bottom mosfet will open. That allows the LC oscillation to go, which the flyback primary being L. When capacitor C voltage sinks to a certain point, the process repeats itself. Or at least that is what I meant for it to do.
uzzors2k, Sun Mar 18 2007, 08:22PM
Nice, I didn't know that about the air gap, I'll have to try it sometime.
Concerning making the circuit self-resonant, I made this on Friday. Its not done yet, as there is still an issue with the high side mosfet floating, but the concept should work. It is supposed to act like a SGTC, except solid state. When circuit starts the top mosfet will conduct until capacitor C is full, at which point it will close and the bottom mosfet will open. That allows the LC oscillation to go, which the flyback primary being L. When capacitor C voltage sinks to a certain point, the process repeats itself. Or at least that is what I meant for it to do.
Re: Flyback output voltage vs. frequency
Sulaiman, Mon Mar 19 2007, 08:06AM
Although I realise it's a conceptual design, there are a few things I notice about the proposed circuit;
1) The diode is unneccessary and will cause the upper mosfet to be on much longer than the lower mosfet
2) The operating voltage for this circuit cannot exceed the Vgs rating of the mosfets
3) The lower mosfet will turn off so slowly (no pull-down resistor) that both mosfets will be on at the same time.
4) Worst of all, BOTH bjts will be on all the time!
Current will flow from +supply via E-B of the pnp to B-E of the npn to 0v.
Not good
Other than the above it should be OK
Sulaiman, Mon Mar 19 2007, 08:06AM
Although I realise it's a conceptual design, there are a few things I notice about the proposed circuit;
1) The diode is unneccessary and will cause the upper mosfet to be on much longer than the lower mosfet
2) The operating voltage for this circuit cannot exceed the Vgs rating of the mosfets
3) The lower mosfet will turn off so slowly (no pull-down resistor) that both mosfets will be on at the same time.
4) Worst of all, BOTH bjts will be on all the time!
Current will flow from +supply via E-B of the pnp to B-E of the npn to 0v.
Not good
Other than the above it should be OK
Re: Flyback output voltage vs. frequency
Ambar, Mon Mar 19 2007, 03:51PM
In ZVS Driver, how much bigger number it of turns in the primario of flyback, and greater the value of the capacitor, greater goes to be the chain and lesser it goes to be the frequency in output high-voltage?
Ambar, Mon Mar 19 2007, 03:51PM
In ZVS Driver, how much bigger number it of turns in the primario of flyback, and greater the value of the capacitor, greater goes to be the chain and lesser it goes to be the frequency in output high-voltage?
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